Our objective is to obtain an understanding of the brain stem mechanisms of facialpain in Macaca mulatta. To this end, we have proposed two temporally overlapping programs of experimentation. The first makes use of the acute preparation to provide definitive electrophysiological information concerning two of the least bulbar structures which are fundamentally involved in trigeminal pain: the somatosensory lateral reticular formation and the dorsolateral zones (laminae I-III) of the trigeminal nucleus caudalis. The second incorporates physiological, lesioning and psychophysical techniques in the awake, unanesthetized monkey to further study the involvement of these structures in facial pain. We anticipate that these structures operate in a regulatory fashion, modulating the centripetal flow of nociceptive information from the periphery. BIBLIOGRAPHIC REFERENCES: Nord, S.G. and R.F. Young. Projection of tooth pulp afferents to the cat trigeminal nucleus caudalis. Brain Res., l975,90:195-204. Young, R.F. and S.G. Nord. modulation stimulation of oro-facial fields. Exper. Neurol. l975, 49:813-821.